WHAT'S IT DO? Under Armour’s most versatile thermal baselayer, the UA Base™ 2.0 1/4 Zip is a must-have for any athlete. Its mid-weight ColdGear® thermal grid fabric is specially engineered to keep your body heat in, while transporting moisture out. The ColdGear® UA Base™ 2.0 Crew also neutralizes odor with anti-microbial technology. So you can concentrate on breaking records, and not on breaking a sweat.